Identify the elements X and Y using the ionization energy values given below:
Ionization energy (kJ/mol)
 

	$1^{st}$	$2^{nd}$
X	495	4563
Y	731	1450

 

For X, $I{P}_1<<<I{P}_2$ Therefore, the second electron is in (n-1) orbit – hence X is Na 

For Y, $I{P}_1<I{P}_2$ Therefore, the second electron is in (n) orbit– hence Y is Mg